One research goal for the second year of this grant is to obtain monoclonal antibody production of Clostridium difficile antitoxin. This specific antitoxin would be useful in the purification of C. difficile toxin because the antibody could be attached to an affinity column, allowing us to use a one-step purification procedure. We also plan to continue studies on the antigenic determinants of the toxins of C. difficile and C. sordellii. We have produced antitoxin to several strains of C. sordellii in our laboratory and have only found slight cross-neutralization (using the mouse lethal assay) of the toxin of C. difficile. C. sordellii standard antitoxin from the U.S. Bureau of Biologics is better for neutralization of C. difficile toxin than any of the C. sordellii antitoxins produced in our laboratory. We still, therefore, need to explain the differences among the antitoxins.